The disclosure relates generally to stators, and more particularly, to a ripple spring having substantially planar end portions to reduce the tendency of abrasion-induced stator winding damage, and a stator bar with a heat resistant and hardened armor layer.
Armature windings, also known as stator bars or windings, are routinely inspected in electrical power generators to verify their operation during scheduled outage. In some generators, a stator yoke in the generator surrounds an armature core and partially encloses the armature windings. The stator windings are formed from a plurality of copper conductors that are wound in the armature to form circuit loops. The armature windings may be arranged within a stator slot in such a manner that the generator may maintain desired voltage, current and service longevity characteristics during operation.
The stator windings of an electric generator are typically under multiple stresses such as electromagnetic and mechanical forces, electric field, chemical and thermal stresses. The mechanical stress imposed on the surface of a stator bar may be laterally, radially and axially applied. Those lateral and radial movements of the bar in the slot are typically restrained with a retention system including ripple springs that induce a radial or circumferential retaining force to the stator to facilitate reducing movement of the stator bar windings within the stator slot.
The modern winding retention system that dampens the lateral movement of a stator winding may employ thousands of ripple springs. The ripple springs that are placed along the stator bars and between the stator core and the bars are called side ripple springs. They are typically compressed approximately 70-90%. A conventional single ripple spring includes ripple waves to absorb the vibration displacement of a stator winding within the ripple amplitude. The forces imposed on the stator bar are relatively high near the end of the slot. Consequently, when a ripple spring wears, the lateral forces of the stator bar may increase the abrasion-related damage to both the spring and armored stator bar surfaces. The phenomenon may reduce the service longevity of a designed stator winding, causing an unscheduled outage, and potentially resulting in a down-time cost. Another abrasion problem may occur when an uneven ripple finish at the edge or end of a side ripple spring wears against the armored glass layer of the stator bar. In this case, the reduced ground wall insulation thickness may increase the frequency and need for repairs or replacement. The stator winding surfaces may also be worn by the ridge of the ripple spring.